The present invention pertains generally to vehicle tires, and more particularly to a new and improved form of tire of the type used primarily on bicycles, wheel chairs, and the like.
Heretofore, the only type of bicycle tire available on the market has been the pneumatic tire, which is constructed much like an automobile tire, with a cord carcass and steel wire beads. Most bicycle tires are of the tube type, and generally, two types of tubes are available; the relatively thin, regular tube, and the considerably heavier, so-called thorn-proof tube.
These pneumatic bicycle tires have a number of disadvantages. They are subject to blow-outs, which cause serious safety hazards. Because of the thin tread, they wear out quickly and have a relatively short service life. Also, as a result of the thin tread, they are readily punctured by thorns and/or small pieces of glass or nails. They lose air and become under-inflated, and as a result they become extremely difficult to ride. It is necessary to carry a tire pump to keep the tires properly inflated, or else make frequent trips to service stations to inflate the tires with their compressed air. The tires are easily cut, and cannot be repaired. They are expensive to manufacture because of the fact that a considerable amount of skilled labor and expensive tooling is required to make the tire. And finally, they do not contribute to the visibility of the bicycle, except when reflective strips are cemented to the side walls of the tires.
There have been attempts to overcome some of the above disadvantages by filling the tires with a mixture of two liquid urethane resins, which react, or cure, to form a solid, resilient elastomeric tire. Such elastomeric tire fillings have been used successfully in automobile tires for a number of years, and two examples of this material are Permatire, made by Arnco, of Marina del Rey, California, and TireFill, made by Indpol, of Cucamonga, California. While bicycle tires filled solidly with urethane rubber eliminate some of the disadvantages of pneumatic tires, such as blow-outs, slow leaks, and underinflation, they have a number of disadvantages of their own. One serious disadvantage is that the urethane-filled tire is extremely heavy, weighing up to 5 or 6 pounds per tire, which makes a total weight penalty of 10 to 12 pounds for the bicycle. This is because it takes from 3 to 4 pounds of urethane rubber to fill the tire. Another disadvantage is that the ride is harder, and rolling resistance is increased. Ride comfort and rolling resistance are mutually antagonistic quantities, and it is necessary to make a compromise between them, which usually results in a fairly hard ride with a moderate amount of rolling resistance.
A more serious problem with filled tires is that they cannot be removed from the wheel rims for spoke repairs or adjustment, without damaging the tire. This is because the tire is filled all the way to the full depth of the rim, which greatly reduces the minimum diameter that has to be pulled over the rim of the wheel. As a result, the only way the tire can be removed is by cutting it, and this destroys the tire.
Another major problem with filled bicycle tires is that wheel rims are easily damaged on sharp impact, due to the incompresssibility of the fill material, which extends directly to the rim. The solid fill material has no place to go, and therefore a sharp impact blow against the tire causes a highly concentrated stress to be applied directly to the rim, causing damage.
The tire filling process is slow, difficult, expensive and unreliable when applied to bicycle tires. It requires equipment to handle liquid urethanes and operators well-trained in handling the polymers to do this filling job right. Bike shops are not set up to do such jobs, and most of them would decline to go into the tire-filling business because of the many problems and relatively small volume of business.
Finally, large cuts cannot be repaired effectively, because the fill material has low physical properties and damages easily when the tire surface is cut.